test(spa): cover lobby->start-round flow without reload (#169)

frontend/tests/vertical-slice.test.ts

@@ -156,4 +156,15 @@ describe('vertical slice controller: lobby -> join -> start round', () => {
     expect(state.startRoundState).toBe('error');
     expect(state.errorMessage).toContain('Kunne ikke starte runden');
   });
+
+  it('uses joined session code when starting round without a reload', async () => {
+    const api = makeApiMock();
+    const controller = createVerticalSliceController(api);
+
+    await controller.joinLobby(' abcd12 ', 'Maja');
+    await controller.startRound('', 'history');
+
+    expect(api.startRound).toHaveBeenCalledWith('ABCD12', { category_slug: 'history' });
+    expect(controller.getState().sessionCode).toBe('ABCD12');
+  });
 });